The invention is directed towards the field of telecommunications, specifically towards incorporating the global positioning system (GPS) into CDMA mobile stations.
When a person calls 911, for emergency assistance, the call is passed along by the telecommunications carrier to the local Public Safety Answering Point (PSAP), which is responsible for dispatching the police, fire and medical services. For a caller from a landline telephone, the PSAP can precisely identify the caller""s location and telephone number even if the caller does not know his or her location. There is a dilemma when the caller is a wireless phone user.
Today, wireless subscribers make a significant number of emergency calls. The PSAPs, however, are unable to pinpoint the location of these callers. Many wireless networks do not provide the PSAP with Automatic Number Identification (ANI) or Automatic Location Identification (ALI). Without the caller""s ANI and ALI, the PSAPs have no way of re-establishing contact with these callers or identifying the location of the caller. This is important in case the call gets cut off and cannot be reestablished by the caller, or for the PSAP to establish the nearest appropriate emergency facility to send. Plus, many wireless users mistakenly believe that their wireless emergency call provides the same functionality as their landline emergency calls have. Incorporating this ANI and ALI into the CDMA mobile transceivers used by the wireless subscriber is an imperative.
In U.S. Pat. No. 6,002,363, xe2x80x9cCombined GPS Positioning System and Communications System Utilizing Shared Circuitryxe2x80x9d, Krasner incorporated GPS into an existing mobile transceiver. Krasner uses a transmit/receive switch that does not require a duplexer to split the transmit and receive paths. His teachings are not compatible for the existing Code Division Multiple Access (CDMA) telecommunications systems because these systems are full duplex systems that must transmit and receive simultaneously.
The present invention incorporates the Global Positioning System (GPS) into mobile telecommunication stations that use Code Division Multiple Access (CDMA) in their operation. Two modes of operation are possible. In the first mode, GPS operation only, there is a temporary cessation of transmission and reception of CDMA telecommunication services to the last base station used. Such instances occur during a xe2x80x9chard handoffxe2x80x9d within the CDMA system. Hand-offs are characterized by a temporary disconnection of the Traffic Channel. In the second mode, CDMA telecommunication transmissions and simultaneous reception of GPS are allowed for. By using the existing CDMA telecommunication channel select filter for GPS operation, there is a significant component cost savings.
Within a housing, the mobile CDMA receiver includes an antenna duplexer, that separates simultaneous CDMA telecommunications transmit and receive signals, connected to an antenna. A CDMA low noise amplifier (LNA) and filter section receives the antenna duplexer output while a GPS bandpass filter receives signals from a GPS antenna. The CDMA section contains a low noise amplifier (CDMA-LNA) connected serially to a radio frequency bandpass filter. The GPS section consists of GPS low noise amplifier positioned between two bandselect filters. A signal path selector receives inputs from either CDMA or GPS. A downconverter utilizes the output of the signal path selector and a local oscillator signal to generate an intermediate frequency (I.F) signal. A 1.23 MHz bandwidth channel select device filters the output of the downconverter, which is then further amplified and processed prior to being sent to a baseband processor for recovery of telecommunication signals or GPS data as required.
In operation, when the mobile receiver is in the CDMA telecommunications mode, the signal path selector accepts inputs from the CDMA-LNA-Bandpass filter and the GPS RF section is powered down. For the CDMA case, the wanted channel in the received RF band is converted to the I.F frequency by the proper selection of the local oscillator (LO) signal applied to the I.F downconverter. The I.F signal is further band limited by the I.F filter, e.g. a surface acoustic wave filter (SAW), having a bandwidth defined by the CDMA mobile system characteristics, typically 1.23 MHz.
During GPS operation, the signal path selected is GPS and the telecommunications CDMA-LNA is powered down. Filtering in the GPS module selects the incoming RF signals within the range of interest centered on 1575.42 MHz or the proposed CA code signal at 1227.60 MHz. The selected range of signals are then downconverted to the same IF frequency as that used for mobile CDMA stations and passed through the same IF filter used by the mobile CDMA telecommunication system. The output from the IF filter is further amplified, processed and passed to the baseband processor where GPS data is recovered.
An alternate embodiment adds a dedicated GPS downconversion mixer and moves the signal path selector to the output side of the CDMA downconversion mixer. This provides for an option of driving the GPS downconversion mixer from either an external, fixed frequency, LO synthesizer, or using the existing CDMA synthesizer by switching the LO signal between either the CDMA or the GPS downconverter LO inputs.